Somatomedin-C will be extracted from Cohn Fraction IV of out-dated human plasma and sufficient quantities carried to purity to complete the sequence analysis. Emphasis will be placed on obtaining sufficient material for both in vivo and in vitro biological studies to determine the range of activities simulated by this growth factor. The nature of somatomedin-C in plasma will be further explored to determine the nature of the non-immunoreactive precursor which has been demonstrated. Further studies of the significance of the somatomedin-C binding protein will be carried out. The role of somatomedin-C in stimulating cell growth will be investigated in cell cultures and emphasis will be placed on the production of somatomedin-C by extrahepatic tissues.